WASHINGTON - US President Donald Trump on Thursday passed up an opportunity to publicly back his embattled Secretary of State, fueling rumors that Rex Tillerson may be on his way out the door.

Asked if he wants Tillerson to remain in his post, Trump said only that “Rex is here” at the White House, a break from the usual expression of confidence in such a circumstances.

A senior White House official did not deny reports that Tillerson would be replaced by CIA director Mike Pompeo - a rumor that has been circulating for months, but which was more firmly reported by the New York Times and other US media earlier Thursday.

The newspaper quoted unnamed senior administration officials as saying Trump had soured on Tillerson and was ready for a change at the State Department, probably around the end of the year. The White House did little to scotch the rumors. “As the President just said, ‘Rex is here,’” said press secretary Sarah Sanders, adding that “there are no personnel announcements at this time.”

“Secretary Tillerson continues to lead the State Department and the entire cabinet is focused on completing this incredibly successful first year of President Trump’s administration.” Trump and Tillerson have aired striking differences in public.

Trump surprised many observers when he tweeted that Tillerson was “wasting his time” pursuing contacts with North Korea, and Tillerson was quoted as having said that the president was a “moron.”

The former ExxonMobil executive has also defended the Iran nuclear deal, which Trump last month disavowed.

It was not clear Thursday whether the president had given final approval to the reported cabinet changes, but he has previously tried to push advisors out rather than sack them outright.

Under the purported plan, Pompeo would be replaced at the CIA by Senator Tom Cotton, a Republican from Arkansas and a hawk on Iran and an important Trump ally on national security issues.

A Cotton aide told AFP that “Senator Cotton’s focus is on serving Arkansans in the Senate.”

His departure would leave Republicans with another seat to defend, at a time when their Senate majority already in question.

Cotton won his seat easily in 2014, and is tipped as a future presidential contender, but Trump’s unpopularity means Republicans can no longer assume victory in even deep red states.

The CIA declined to comment.

Analysts saw the move as evidence that Trump is trying to take more control over foreign policy.

“Trump is trying to find a way to hire people who are loyal to him and will help him push back against the establishment,” Thomas Wright of the Brookings Institution told AFP.

“Pompeo and Cotton have both convinced Trump they fit the bill,” he added. “Overall, it’s a sign that Trump wants more control over his own foreign policy.”